Weight Loss Tied to a Dramatic Drop in Cancer Risk, New Study Shows

According to the CDC, people with obesity tend to have higher levels of hormones such as insulin and insulin-like growth factor-1, or IGF-1, which can stimulate the development of colon, kidney, prostate and endometrial cancers.

Bariatric surgery can result in significant weight loss. Although some patients eventually regain some of the weight they lost, studies show that most people who undergo bariatric surgery can maintain a greater than 20 percent reduction in their body weight a decade after their procedure. This is far greater than what people with obesity can typically lose and maintain through diet and exercise alone.

For the new study, Dr. Nissen and his colleagues wanted to see how that amount of weight loss would affect cancer rates. They recruited and followed 5,053 people with obesity who underwent bariatric surgery at the Cleveland Clinic. Each patient was “matched” with five other patients who were similar in many ways. They were about the same age, sex, and race, and they had similar medical histories and body mass indexes, but they had not undergone weight loss surgery.

In total, there were more than 30,000 participants in the study, which included 25,265 people in the control group. Both groups had a median age of 46 and a median body mass index of 45, which the CDC categorizes as “severe” obesity. This is the equivalent of someone who is 5 feet 8 inches tall and weighs about 300 pounds. According to the CDC, someone with a BMI between 25 and 30 is considered overweight and someone with a BMI above 30 is classified as obese. A large nationwide study published last year found that about 42 percent of adults in the United States were obese and about 9 percent had severe obesity.

Not every person with obesity can undergo weight loss surgery. Generally, to qualify, patients must have a BMI of at least 40, or a BMI of 35 or higher along with at least one obesity-related condition, such as type 2 diabetes, hypertension or heart disease. In the new study, people who had surgery had either gastric bypass or sleeve gastrectomy procedures.

After a decade, the patients who had the surgery lost an average of about 61 pounds, while those in the control group (who were advised by their doctors to try to lose weight on their own) lost an average of six pounds. Slightly less than 3 percent of patients who had surgery developed cancer, compared with about 4.9 percent of those in the non-surgical group—equivalent to a 32 percent reduction in risk for those who had surgery.

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